Enabling DisplayPort in the OSD menu of the monitor *Dell UP3214Q* supports 3840 x 2160 at 60 Hz [1]. But that monitor has two panels, and uses Multi-Stream Transport [2]. > DisplayPort 1.2 added support for Multi-Stream Transport (MST), enabling multiple monitors to be used via a single DisplayPort connector. This function requires either monitors that are capable of DisplayPort 1.2 daisy-chaining, or use of a DisplayPort MST Hub. The first MST hub became available in September 2013, enabling up to 3 displays to be connected to a single DisplayPort connector.[33] > > Single Stream Transport (SST) was specified in DisplayPort 1.1a for use between a single Source and Sink Device. Xrandr 1.5 [1] adds support for these kinds of displays by introducing monitor objects [4]. ``` $ xrandr --listmonitors Monitors: 1 0: +Auto-Monitor-1 3840/698x2160/392+0+0 DP-2-9 DP-2-8 ``` Currently, Xfce shows two desktops on the Dell monitor, while it should be just one. [1] https://bugs.freedesktop.org/show_bug.cgi?id=103768 [2] https://en.wikipedia.org/wiki/DisplayPort#Multiple_displays_on_single_DisplayPort_connector [3] https://lists.freedesktop.org/archives/xorg-announce/2016-February/002677.html [4] https://github.com/i3/i3/issues/2909
This seems to work with Xfdesktop 4.13.x. There seem to be some driver issues with MST displays, but these should be tracked separately.
For the record, the AMDGPU driver does not support this including version 19.0.0. The support is implemented in [1]. [1]: https://gitlab.freedesktop.org/xorg/driver/xf86-video-amdgpu/merge_requests/32